Semiconductor device

ABSTRACT

A semiconductor device includes a barrier layer, a channel layer, a regrowth layer, a vacancy generation region, and a source electrode or a drain electrode. The barrier layer includes a first nitride semiconductor. The channel layer includes a second nitride semiconductor and is bonded to the barrier layer at a first surface. The regrowth layer includes an n-type nitride semiconductor and is provided in a region dug deeper than an interface between the barrier layer and the channel layer from a second surface of the barrier layer. The second surface is on opposite side to the first surface. The vacancy generation region includes a nitrogen-capturing element and is provided in a region of the regrowth layer shallower than the interface between the barrier layer and the channel layer. The source electrode or the drain electrode is provided on the regrowth layer.

TECHNICAL FIELD

The present disclosure relates to a semiconductor device.

BACKGROUND ART

Recently, a high electron mobility transistor (High Electron MobilityTransistor: HEMT) using a nitride semiconductor has been put intopractical use in applications such as power amplifiers (for example, PTL1). The high electron mobility transistor is a field-effect transistorin which a two-dimensional electron gas layer formed at an interface ofa heterojunction of the nitride semiconductor is used as a channel.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2019-192698

SUMMARY OF THE INVENTION

However, because a nitride semiconductor used in a high electronmobility transistor is a wide-band-gap semiconductor, it is difficult toform a low-resistance ohmic contact with an electrode. Accordingly,regarding the high electron mobility transistor, it is desired todecrease resistance between a channel formed at an interface of aheterojunction of the nitride semiconductor and the electrode.

It is therefore desirable to provide a semiconductor device in whichresistance between an electrode and a channel is further decreased.

A semiconductor device according to an embodiment of the presentdisclosure includes a barrier layer, a channel layer, a regrowth layer,a vacancy generation region, and a source electrode or a drainelectrode. The barrier layer includes a first nitride semiconductor. Thechannel layer includes a second nitride semiconductor and is bonded tothe barrier layer at a first surface. The regrowth layer includes ann-type nitride semiconductor and is provided in a region dug deeper thanan interface between the barrier layer and the channel layer from asecond surface of the barrier layer. The second surface is on oppositeside to the first surface. The vacancy generation region includes anitrogen-capturing element and is provided in a region of the regrowthlayer shallower than the interface between the barrier layer and thechannel layer. The source electrode or the drain electrode is providedon the regrowth layer.

In the semiconductor device according to the embodiment of the presentdisclosure, the vacancy generation region including thenitrogen-capturing element is provided in the region of the regrowthlayer shallower than the interface between the channel layer and thebarrier layer. The barrier layer and the channel layer are partially dugto form the regrowth layer. As a result, for example, the vacancygeneration region is able to form a vacancy serving as a doner in theregrowth layer below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical sectional view of a configuration of asemiconductor device according to a first embodiment of the presentdisclosure.

FIG. 2 is a schematic energy band diagram illustrating workings andeffects of the semiconductor device according to the embodiment.

FIG. 3 is a graph illustrating a relationship between a depth at which asource electrode or a drain electrode is formed from a surface of abarrier layer as a base (zero point) and contact resistance of thesource electrode or the drain electrode.

FIG. 4A is a vertical sectional view of a process of a method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 4B is a vertical sectional view of a process of the method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 4C is a vertical sectional view of a process of the method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 4D is a vertical sectional view of a process of the method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 4E is a vertical sectional view of a process of the method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 4F is a vertical sectional view of a process of the method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 5 is a vertical sectional view of a configuration of asemiconductor device according to a second embodiment of the presentdisclosure.

FIG. 6 is a graph illustrating variation in contact resistance due topresence or absence of a low defect region.

FIG. 7A is a vertical sectional view of a process of a method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 7B is a vertical sectional view of a process of the method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 7C is a vertical sectional view of a process of the method ofmanufacturing the semiconductor device according to the embodiment.

FIG. 8 is a block diagram depicting an example of schematicconfiguration of a vehicle control system.

FIG. 9 is a diagram of assistance in explaining an example ofinstallation positions of an outside-vehicle information detectingsection and an imaging section.

MODES FOR CARRYING OUT THE INVENTION

Some embodiments of the present disclosure are described below in detailwith reference to the drawings. The embodiments described below arespecific examples of the present disclosure, and the technique accordingto the present disclosure is not limited to the following embodiments.In addition, arrangements, dimensions, dimension ratios, etc. ofrespective components of the present disclosure are not limited to theembodiments illustrated in respective drawings.

It is to be noted that the description is given in the following order.

-   1. First Embodiment    -   1.1. Configuration    -   1.2. Manufacturing Method-   2. Second Embodiment    -   2.1. Configuration    -   2.2. Manufacturing Method-   3. Application Examples

<1. First Embodiment>

First, referring to FIG. 1 , described is a configuration of asemiconductor device according to a first embodiment of the presentdisclosure. FIG. 1 is a vertical sectional view of a configuration of asemiconductor device 100 according to the present embodiment.

As illustrated in FIG. 1 , the semiconductor device 100 includes asubstrate 110, a channel layer 120, a barrier layer 130, a regrowthlayer 140 including a vacancy generation region 141, a source electrode150S, a drain electrode 150D, an insulation layer 160, and a gateelectrode 170.

The semiconductor device 100 is a high electron mobility transistor thatuses, as a channel, a two-dimensional electron gas layer (2DEG) formedby a difference between the magnitude of polarization of the channellayer 120 and the magnitude of polarization of the barrier layer 130.The two-dimensional electron gas layer is formed, for example, in thevicinity of the barrier layer 130 in the channel layer 120.

The substrate 110 is a support body for epitaxially growing the channellayer 120 and the barrier layer 130. Specifically, the substrate 110 maybe a substrate including a semiconductor material having a latticeconstant close to that of a nitride semiconductor included in thechannel layer 120. For example, the substrate 110 may be a substrateincluding a III-V compound semiconductor such as a single-crystal GaNsubstrate.

It is to be noted that the semiconductor device 100 may further includea buffer layer between the substrate 110 and the channel layer 120. Thebuffer layer includes a semiconductor material having a lattice constantclose to that of the channel layer 120. The buffer layer is able to makemore favorable a crystalline state of the channel layer 120 and tosuppress warpage of the substrate 110 by controlling a lattice constantof a surface on which the channel layer 120 is epitaxially grown.

In addition, in a case where the buffer layer is provided, the substrate110 may be a substrate including a material having a lattice constantdifferent from that of the nitride semiconductor included in the channellayer 120. Specifically, the substrate 110 may be, for example, a SiCsubstrate, a sapphire substrate, a Si substrate, or the like. Forexample, in a case where the substrate 110 is a single-crystal Sisubstrate, providing a buffer layer including AlN, AlGaN, or GaN betweenthe substrate 110 and the channel layer 120 makes it possible toepitaxially grow the channel layer 120 including GaN with a morefavorable crystalline state in the semiconductor device 100.

The channel layer 120 includes a nitride semiconductor having a band gapnarrower than that of the barrier layer 130. The channel layer 120 isable to accumulate carriers on the channel layer 120 side in thevicinity of the interface between it and the barrier layer 130 due tothe difference in the magnitude of polarization between it and thebarrier layer 130. For example, the channel layer 120 may includeepitaxially grown GaN. Alternatively, the channel layer 120 may includeundoped u-GaN with no impurity added. In such a case, the channel layer120 is able to suppress impurity scattering of carriers, and istherefore able to further increase mobility of the carriers.

The barrier layer 130 includes a nitride semiconductor having a band gapwider than that of the channel layer 120. By being bonded to the channellayer 120, the barrier layer 130 is able to allow the carriers to beaccumulated in the channel layer 120 in the vicinity of the barrierlayer 130 by spontaneous polarization or piezoelectric polarization.Thus, the two-dimensional electron gas layer having high mobility andhigh carrier concentration is formed in the vicinity of the barrierlayer 130 in the channel layer 120.

For example, the barrier layer 130 may include epitaxially grownAl_(1-x-y)Ga_(x)In_(y)N (where 0 ≤ x < 1 and 0 ≤ y < 1). Alternatively,the barrier layer 130 may include undoped u-Al_(1-x-y)Ga_(x)In_(y)N withno impurity added.

It is to be noted that the barrier layer 130 may include a single layer,or may be provided by stacking a plurality of layers ofAl_(1-x-y)Ga_(x)In_(y)N different in composition. In addition, thebarrier layer 130 may be configured in such a manner that itscomposition gradually changes in a thickness direction.

It is to be noted that, although not illustrated, an active region andan element separation region are each provided in an in-plane directionof the substrate 110 for a stack structure including the substrate 110,the channel layer 120, and the barrier layer 130.

The active region is a region in which each configuration of thesemiconductor device 100 is provided, and is formed as an island-shapedregion surrounded by the element separation region. The elementseparation region is formed by inactivating the channel layer 120 andthe barrier layer 130 by ion implantation using B (boron) or the like.The element separation region is provided to surround the active regionand is able to electrically isolate active regions from each other. Itis to be noted that the element separation region may be formed byremoving the channel layer 120 and the barrier layer 130 by means ofetching.

The insulation layer 160 includes an insulating material and is providedon the barrier layer 130. For example, the insulation layer 160 may beprovided as, for example, a single-layer film of SiO₂, SiN, SION, Al₂O₃,or HfO₂ having an insulating property with respect to the barrier layer130, or a multilayer stacked film thereof. The insulation layer 160protects a surface of the barrier layer 130 from impurities such as ionsand makes favorable an interface between it and the barrier layer 130,to thereby suppress a decrease in properties of the semiconductor device100.

The gate electrode 170 includes an electrically conductive material andis provided on the insulation layer 160. For example, the gate electrode170 may be provided by stacking Ni (nickel) and Au (gold) from theinsulation layer 160 side.

The gate electrode 170 is able to control the carrier concentration ofthe two-dimensional electron gas layer formed in the channel layer 120by means of an applied voltage. Specifically, the gate electrode 170 isable to control the carrier concentration of the two-dimensionalelectron gas layer formed in the channel layer 120 by means of a fieldeffect by controlling the thickness of a depletion layer formed in thebarrier layer 130 below by means of the applied voltage.

The regrowth layer 140 is provided, for example, by performing diggingfrom the barrier layer 130 side to a region deeper than the interfacebetween the barrier layer 130 and the channel layer 120, and filling thedug region with an n-type nitride semiconductor. Specifically, theregrowth layer 140 is provided by partially removing the barrier layer130 and the channel layer 120 by means of etching or the like to form anopening, and thereafter selectively epitaxially growing a nitridesemiconductor including an n-type impurity in the opening. The regrowthlayer 140 including the n-type impurity has electrical conductivityhigher than that of the barrier layer 130. Therefore, it is possible toelectrically couple the source electrode 150S and the drain electrode150D, and the two-dimensional electron gas layer with low resistance.For example, the regrowth layer 140 may include In_(1-x)Ga_(x)Nincluding an n-type impurity such as Si or Ge at 1.0 × 10¹⁸/cm³ or more.

The source electrode 150S and the drain electrode 150D are provided onthe respective regrowth layers 140 provided on both sides of the gateelectrode 170. The source electrode 150S and the drain electrode 150Dare each able to be electrically coupled to the two-dimensional electrongas layer in the channel layer 120 via the regrowth layer 140. Thesource electrode 150S and the drain electrode 150D may be provided witha structure in which Ti (titanium), Al (aluminum), Ni (nickel), and Au(gold) are stacked sequentially from the regrowth layer 140 side.

In the semiconductor device 100 according to the present embodiment, theregrowth layer 140 further includes a vacancy generation region 141including a nitrogen-capturing element. The vacancy generation region141 is provided in a region, of the regrowth layer 140, that is on aside in contact with the source electrode 150S and the drain electrode150D and that is shallower than the interface between the barrier layer130 and the channel layer 120.

In the vacancy generation region 141, the contained nitrogen-capturingelement is bonded to nitrogen of the n-type nitride semiconductor,making it possible to generate a nitrogen vacancy in the regrowth layer140. Specifically, the vacancy generation region 141 is able to extractnitrogen from the regrowth layer 140 below the vacancy generation region141 by the nitrogen-capturing element, therefore being able to generatea nitrogen vacancy serving as a doner in the regrowth layer 140 belowthe vacancy generation region 141. Thus, the vacancy generation region141 is able to improve electrical conductivity of the regrowth layer 140below the vacancy generation region 141. Accordingly, it is possible tofurther decrease the contact resistance from the two-dimensionalelectron gas layer to the source electrode 150S or the drain electrode150D.

Referring to FIG. 2 , workings and effects of the vacancy generationregion 141 are described more specifically. FIG. 2 is a schematic energyband diagram illustrating the workings and effects of the semiconductordevice 100 according to the present embodiment. It is to be noted that,in FIG. 2 , E_(c) represents an energy level of a lower end of aconduction band, E_(v) represents an energy level of an upper end of avalence band, and E_(f) represents a Fermi level.

As illustrated in FIG. 2 , at the interface between the vacancygeneration region 141 and the regrowth layer 140, nitrogen atoms N_(N)are extracted from the regrowth layer 140 by the nitrogen-capturingelement included in the vacancy generation region 141, and the nitrogenvacancies V_(N) are thereby generated in the regrowth layer 140. Thegenerated nitrogen vacancies V_(N) serve as donors and decrease theenergy level of the regrowth layer 140, thereby making it possible tolower an energy barrier between the two-dimensional electron gas layer(2DEG) formed at the interface between the channel layer 120 and thebarrier layer 130, and the regrowth layer 140. As a result, due to atunnel effect, contact resistance R₂ between the source electrode 150Sor the drain electrode 150D and the regrowth layer 140 is decreased, andcontact resistance R₁ between the regrowth layer 140 and thetwo-dimensional electron gas layer serving as a channel is alsodecreased. Accordingly, the regrowth layer 140 is able to form alow-resistance contact from the source electrode 150S or the drainelectrode 150D to the two-dimensional atomic gas layer serving as achannel.

The nitrogen-capturing element contained in the vacancy generationregion 141 is, for example, Ti (titanium) or Al (aluminum). Ti and Alare able to form a nitride by being bonded to N (nitrogen), and aretherefore able to extract N from a region adjacent to the vacancygeneration region 141 of the regrowth layer 140. Further, in thesemiconductor device 100, configuring the source electrode 150S or thedrain electrode 150D to include Ti or Al makes it possible to diffuse Tior Al from the source electrode 150S or the drain electrode 150D intothe regrowth layer 140 to form the vacancy generation region 141. Insuch a case, it is possible to form the vacancy generation region 141 inthe regrowth layer 140 in the semiconductor device 100 withoutperforming any additional process.

It is to be noted that, as described above, the vacancy generationregion 141 may be formed by diffusing the nitrogen-capturing element(e.g., Ti, Al, or the like) from the source electrode 150S or the drainelectrode 150D into the regrowth layer 140; however, the vacancygeneration region 141 may be formed by any other method. For example,the vacancy generation region 141 may be formed by implanting thenitrogen-capturing element (e.g., Ti, Al, or the like) into the regrowthlayer 140 by ion implantation or the like.

Now, referring to FIG. 3 , described is the depth at which the vacancygeneration region 141 is formed. FIG. 3 is a graph illustrating arelationship between a depth at which the source electrode 150S or thedrain electrode 150D is formed from the surface of the barrier layer 130as a base (a zero point) and contact resistance of the source electrode150S or the drain electrode 150D. It is to be noted that the vacancygeneration region 141 is formed immediately below the source electrode150S or the drain electrode 150D by diffusing Ti from the sourceelectrode 150S or the drain electrode 150D.

FIG. 3 illustrates a measurement result of the semiconductor device 100in which the thickness of the barrier layer 130 is 10 nm. Further, FIG.3 describes contact resistance by a relative value where that in a casewhere the depth at which the source electrode 150S or the drainelectrode 150D is formed is 0 nm (that is, a case where the sourceelectrode 150S or the drain electrode 150D is formed at the same surfaceheight as the surface of the barrier layer 130) is regarded as 1.

As illustrated in FIG. 3 , in a case where the depth at which the sourceelectrode 150S or the drain electrode 150D is formed is 5 nm, thecontact resistance of the source electrode 150S or the drain electrode150D is remarkably decreased. Because the thickness of the barrier layer130 is 10 nm, in this case, the vacancy generation region 141 is formedin a region shallower than the interface between the barrier layer 130and the channel layer 120.

In contrast, in a case where the depth at which the source electrode150S or the drain electrode 150D is formed is 25 nm, the contactresistance of the source electrode 150S or the drain electrode 150D isincreased. Because the thickness of the barrier layer 130 is 10 nm, inthis case, the vacancy generation region layer 141 is formed in a regiondeeper than the interface between the barrier layer 130 and the channellayer 120.

This is because the vacancy generation region 141 forms a vacancy whichserves as a donor in the regrowth layer 140 below. By being provided ina region shallower than the interface between the barrier layer 130 andthe channel layer 120, the vacancy generation region 141 is able to forma vacancy serving as a doner in a region in contact with the interfacebetween the channel layer 120 and the barrier layer 130 (i.e., thetwo-dimensional electron gas layer).

According to the semiconductor device 100 of the first embodiment, thevacancy generation region 141 is provided, which makes it possible toform a vacancy serving as a donor in the regrowth layer 140. Therefore,the semiconductor device 100 is able to further enhance the electricalconductivity of the regrowth layer 140. Accordingly, it is possible todecrease the resistance from the two-dimensional electron gas layer tothe source electrode 150S or the drain electrode 150D.

(1.2. Manufacturing Method)

Referring to FIGS. 4A to 4F, described is an example of a method ofmanufacturing the semiconductor device 100 according to the presentembodiment. FIGS. 4A to 4F are each a vertical sectional viewillustrating each process of the method of manufacturing thesemiconductor device 100 according to the present embodiment.

First, as illustrated in FIG. 4A, for example, GaN is epitaxially grownon the substrate 110 including GaN or the like to thereby form thechannel layer 120. Thereafter, AlGaN (Al_(0.3)-Ga_(0.7)N mixed crystal)is epitaxially grown on the channel layer 120 to thereby form thebarrier layer 130.

Thereafter, although not illustrated, B (boron) is ion-implanted into apredetermined planar region of the barrier layer 130 and the channellayer 120 to thereby form an element separation region in which theresistance of the barrier layer 130 and the channel layer 120 isincreased. For example, the element separation region is so formed as tosurround the periphery of the island-shaped active region, andelectrically isolates active regions from each other. It is to be notedthat the element separation region may be formed at any timing such as atiming after the formation of the source electrode 150S and the drainelectrode 150D, or a timing after the formation of the gate electrode170, which will be described later.

Thereafter, as illustrated in FIG. 4B, the barrier layer 130 and thechannel layer 120 are partially removed by etching to form an opening140H for selectively growing the regrowth layer 140 in a later process.A region to form the opening 140H corresponds to a region to form thesource electrode 150S and the drain electrode 150D in a later process.

Thereafter, as illustrated in FIG. 4C, InGaN including an n-typeimpurity such as Si or Ge is selectively epitaxially grown to fill theopening 140H, to thereby form the regrowth layer 140.

Thereafter, as illustrated in FIG. 4D, the source electrode 150S and thedrain electrode 150D are formed on the regrowth layer 140. Specifically,Ti (titanium), Al (aluminum), Ni (nickel), and Au (gold) aresequentially deposited on the regrowth layer 140 and thereafterpatterned to thereby form the source electrode 150S and the drainelectrode 150D.

Accordingly, as illustrated in FIG. 4E, Ti (titanium) is diffused fromthe source electrode 150S and the drain electrode 150D into the regrowthlayer 140. As a result, the vacancy generation region 141 is formed inthe regrowth layer 140. The vacancy generation region 141 is formed in aregion into which Ti is diffusible from the source electrode 150S andthe drain electrode 150D. Therefore, the vacancy generation region 141is provided in a region shallower than the interface between the channellayer 120 and the barrier layer 130.

Thereafter, as illustrated in FIG. 4F, the insulation layer 160 and thegate electrode 170 are formed on the barrier layer 130.

Specifically, first, a film of SiO₂ (silicon dioxide) or the like isformed on the barrier layer 130 by a CVD (Chemical Vapor Deposition)method except for a region provided with the source electrode 150S andthe drain electrode 150D, to thereby form the insulation layer 160. Itis to be noted that the insulation layer 160 may be provided by forminga film of Al₂O₃ (aluminum oxide) by an ALD (Atomic Layer Deposition)method, or may be provided by forming a film of SiN (silicon nitride) bya CVD method. Alternatively, the insulation layer 160 may be provided bystacking a plurality of layers including the above-described materials.

Thereafter, the gate electrode 170 is formed on the insulation layer 160between the source electrode 150S and the drain electrode 150D.Specifically, Ni (nickel) and Au (gold) are sequentially deposited onthe insulation layer 160 and thereafter patterned to thereby form thegate electrode 170.

By the above-described processes, it is possible to form thesemiconductor device 100 according to the present embodiment.

<2. Second Embodiment> (2.1. Configuration)

Next, referring to FIG. 5 , described is a configuration of asemiconductor device according to a second embodiment of the presentdisclosure. FIG. 5 is a vertical sectional view of a configuration of asemiconductor device 101 according to the present embodiment.

As illustrated in FIG. 5 , as compared with the semiconductor device 100according to the first embodiment, the semiconductor device 101according to the second embodiment is different in that a low defectregion 142 is further provided in a region, of the regrowth layer 140,in contact with the interface between the channel layer 120 and thebarrier layer 130.

The low defect region 142 is a region having a crystal defect densitylower than that in other regions of the regrowth layer 140. The lowdefect region 142 is provided in a region, of the regrowth layer 140, incontact with the interface between the channel layer 120 and the barrierlayer 130, extending toward the channel layer 120 side.

The low defect region 142 is able to facilitate injection of carriersfrom the source electrode 150S to the two-dimensional electron gas layer(2DEG) formed at the interface between the channel layer 120 and thebarrier layer 130, and also facilitate discharging of carriers from thetwo-dimensional electron gas layer to the drain electrode 150D.

For example, in a case where the crystal defect density is 1.0 ×10⁸/cm², the size of a region in which carriers injected from thetwo-dimensional electron gas layer serving as a channel are movablewithout being influenced by a crystal defect is about 1 µm square. Inaddition, the size of the region in which the carriers are movablewithout being influenced by a crystal defect decreases as the crystaldefect density increases. In a case where the crystal defect density is1.0 × 10⁹/cm², the size of the region is about 300 nm square. In a casewhere the crystal defect density is 1.0 × 10¹⁰/cm², the size of theregion is about 100 nm square. In a case where the crystal defectdensity is 1.0 × 10¹¹/cm², the size of the region is less than 30 nmsquare.

In GaN which is a typical nitride semiconductor, a mean free path ofcarriers having energy of 1 eV is about 14 nm. Therefore, it isconceivable that if the crystal defect density in the low defect region142 is 1.0 × 10¹⁰/cm² or less, carriers injected from the channel to thelow defect region 142 are able to move without being influenced by acrystal defect with high probability. Accordingly, providing the lowdefect region 142 in a region in contact with the interface between thechannel layer 120 and the barrier layer 130 makes it possible for theregrowth layer 140 to further decrease the contact resistance from thechannel to the source electrode 150S or the drain electrode 150D.

It is possible to calculate the crystal defect density of the low defectregion 142, for example, from an image captured by TEM (TransmissionElectron Microscope). In the image captured by TEM, the crystal defectis observed as a change in brightness in the captured image. Therefore,it is possible to calculate the crystal defect density from the imagecaptured by TEM.

Here, referring to FIG. 6 , described is a decrease in the contactresistance due to the low defect region 142. FIG. 6 is a graphillustrating variation in the contact resistance due to presence orabsence of the low defect region 142.

FIG. 6 illustrates variation in the contact resistance due to thepresence or the absence of the low defect region 142 having the crystaldefect density of 1.0 × 10¹⁰/cm² or less. It is to be noted that FIG. 6describes the contact resistance by a relative value where that in acase where no low defect region 142 is provided is regarded as 1.

As illustrated in FIG. 6 , it can be appreciated that, as compared withthe case where no low defect region 142 is provided, in a case where thelow defect region 142 is provided, the contact resistance decreases byabout 20% in the semiconductor device 101.

According to the semiconductor device 101 of the second embodiment, thelow defect region 142 is provided in a region in contact with theinterface between the channel layer 120 and the barrier layer 130, whichmakes it possible to further facilitate the injection of the carriersfrom the regrowth layer 140 to the two-dimensional electron gas layerand the discharging of the carriers from the two-dimensional electrongas layer to the regrowth layer 140. Accordingly, it is possible tofurther decrease the resistance between the two-dimensional electron gaslayer and the source electrode 150S or the drain electrode 150D in thesemiconductor device 101.

(2.2. Manufacturing Method)

Referring to FIGS. 7A to 7C, described is a method of manufacturing thesemiconductor device 101 according to the present embodiment. FIGS. 7Ato 7C are each a vertical sectional view of each process of the methodof manufacturing the semiconductor device 101 according to the presentembodiment.

First, through processes similar to the processes illustrated in FIGS.4A and 4B, a stack structure including the substrate 110, the channellayer 120, and the barrier layer 130 is formed, and the opening 140H forforming the regrowth layer 140 is formed in the stack structure.

Thereafter, as illustrated in FIG. 7A, an underlayer 145 is provided ona bottom surface in a region, of the opening 140H, in contact with theinterface between the channel layer 120 and the barrier layer 130. Forexample, the underlayer 145 includes SiN and is provided to mask thechannel layer 120 in the region in contact with the interface betweenthe channel layer 120 and the barrier layer 130.

Thereafter, as illustrated in FIG. 7B, the regrowth layer 140 isselectively epitaxially grown in the opening 140H with the underlayer145 being provided. At this time, because the regrowth layer 140 isunable to be epitaxially grown from the channel layer 120 on theunderlayer 145, crystal growth occurs laterally in an in-plane directionof the bottom surface of the opening 140H, and the regrowth layer 140 isthus formed on the underlayer 145. This allows the regrowth layer 140,which is provided on the underlayer 145, to be formed without takingover a crystal defect present in the channel layer 120. Therefore, theregrowth layer 140 provided on the underlayer 145 is provided to have acrystal defect density lower than that in other regions of the regrowthlayer 140.

Thus, as illustrated in FIG. 7C, the regrowth layer 140 in the region onthe underlayer 145 is provided with a lower crystal defect densitywithout taking over the crystal defect present in the channel layer 120.Accordingly, the regrowth layer 140 in the region on the underlayer 145is provided as the low defect region 142.

By the above-described processes, it is possible to form the regrowthlayer 140 including the low defect region 142. After the regrowth layer140 is formed, the source electrode 150S and the drain electrode 150Dare formed on the regrowth layer 140, and the insulation layer 160 andthe gate electrode 170 are formed on the barrier layer 130 by processessimilar to those illustrated in FIGS. 4D to 4F.

<3. Application Examples>

The technique according to the present disclosure described above isable to be favorably used in amplification of a high-frequency signal.Specifically, the semiconductor devices 100 and 101 according to thefirst and second embodiments of the present disclosure are able to befavorably used in an amplification circuit for a high-frequency signalof a vehicle-mounted ranging sensor using a millimeter wave.

For example, the technique according to the present disclosure may beapplied to a ranging sensor to be provided on any kind of mobile bodies,including automobiles, electric vehicles, hybrid electric vehicles,motorcycles, bicycles, personal mobilities, aircrafts, drones, vessels,robots, and the like. Specifically described below is an example of acontrol system for a mobile body to which the technique according to thepresent disclosure is applicable.

FIG. 8 is a block diagram depicting an example of schematicconfiguration of a vehicle control system as an example of a mobile bodycontrol system to which the technology according to an embodiment of thepresent disclosure can be applied.

The vehicle control system 12000 includes a plurality of electroniccontrol units connected to each other via a communication network 12001.In the example depicted in FIG. 8 , the vehicle control system 12000includes a driving system control unit 12010, a body system control unit12020, an outside-vehicle information detecting unit 12030, anin-vehicle information detecting unit 12040, and an integrated controlunit 12050. In addition, a microcomputer 12051, a sound/image outputsection 12052, and a vehicle-mounted network interface (I/F) 12053 areillustrated as a functional configuration of the integrated control unit12050.

The driving system control unit 12010 controls the operation of devicesrelated to the driving system of the vehicle in accordance with variouskinds of programs. For example, the driving system control unit 12010functions as a control device for a driving force generating device forgenerating the driving force of the vehicle, such as an internalcombustion engine, a driving motor, or the like, a driving forcetransmitting mechanism for transmitting the driving force to wheels, asteering mechanism for adjusting the steering angle of the vehicle, abraking device for generating the braking force of the vehicle, and thelike.

The body system control unit 12020 controls the operation of variouskinds of devices provided to a vehicle body in accordance with variouskinds of programs. For example, the body system control unit 12020functions as a control device for a keyless entry system, a smart keysystem, a power window device, or various kinds of lamps such as aheadlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, or thelike. In this case, radio waves transmitted from a mobile device as analternative to a key or signals of various kinds of switches can beinput to the body system control unit 12020. The body system controlunit 12020 receives these input radio waves or signals, and controls adoor lock device, the power window device, the lamps, or the like of thevehicle.

The outside-vehicle information detecting unit 12030 detects informationabout the outside of the vehicle including the vehicle control system12000. For example, the outside-vehicle information detecting unit 12030is connected with an imaging section 12031. The outside-vehicleinformation detecting unit 12030 makes the imaging section 12031 imagean image of the outside of the vehicle, and receives the imaged image.On the basis of the received image, the outside-vehicle informationdetecting unit 12030 may perform processing of detecting an object suchas a human, a vehicle, an obstacle, a sign, a character on a roadsurface, or the like, or processing of detecting a distance thereto.

The imaging section 12031 is an optical sensor that receives light, andwhich outputs an electric signal corresponding to a received lightamount of the light. The imaging section 12031 can output the electricsignal as an image, or can output the electric signal as informationabout a measured distance. In addition, the light received by theimaging section 12031 may be visible light, or may be invisible lightsuch as infrared rays or the like.

The in-vehicle information detecting unit 12040 detects informationabout the inside of the vehicle. The in-vehicle information detectingunit 12040 is, for example, connected with a driver state detectingsection 12041 that detects the state of a driver. The driver statedetecting section 12041, for example, includes a camera that images thedriver. On the basis of detection information input from the driverstate detecting section 12041, the in-vehicle information detecting unit12040 may calculate a degree of fatigue of the driver or a degree ofconcentration of the driver, or may determine whether the driver isdozing.

The microcomputer 12051 can calculate a control target value for thedriving force generating device, the steering mechanism, or the brakingdevice on the basis of the information about the inside or outside ofthe vehicle which information is obtained by the outside-vehicleinformation detecting unit 12030 or the in-vehicle information detectingunit 12040, and output a control command to the driving system controlunit 12010. For example, the microcomputer 12051 can perform cooperativecontrol intended to implement functions of an advanced driver assistancesystem (ADAS) which functions include collision avoidance or shockmitigation for the vehicle, following driving based on a followingdistance, vehicle speed maintaining driving, a warning of collision ofthe vehicle, a warning of deviation of the vehicle from a lane, or thelike.

In addition, the microcomputer 12051 can perform cooperative controlintended for automated driving, which makes the vehicle to travelautomatedly without depending on the operation of the driver, or thelike, by controlling the driving force generating device, the steeringmechanism, the braking device, or the like on the basis of theinformation about the outside or inside of the vehicle which informationis obtained by the outside-vehicle information detecting unit 12030 orthe in-vehicle information detecting unit 12040.

In addition, the microcomputer 12051 can output a control command to thebody system control unit 12020 on the basis of the information about theoutside of the vehicle which information is obtained by theoutside-vehicle information detecting unit 12030. For example, themicrocomputer 12051 can perform cooperative control intended to preventa glare by controlling the headlamp so as to change from a high beam toa low beam, for example, in accordance with the position of a precedingvehicle or an oncoming vehicle detected by the outside-vehicleinformation detecting unit 12030.

The sound/image output section 12052 transmits an output signal of atleast one of a sound and an image to an output device capable ofvisually or auditorily notifying information to an occupant of thevehicle or the outside of the vehicle. In the example of FIG. 8 , anaudio speaker 12061, a display section 12062, and an instrument panel12063 are illustrated as the output device. The display section 12062may, for example, include at least one of an on-board display and ahead-up display.

FIG. 9 is a diagram depicting an example of the installation position ofthe imaging section 12031.

In FIG. 9 , the imaging section 12031 includes imaging sections 12101,12102, 12103, 12104, and 12105.

The imaging sections 12101, 12102, 12103, 12104, and 12105 are, forexample, disposed at positions on a front nose, sideview mirrors, a rearbumper, and a back door of the vehicle 12100 as well as a position on anupper portion of a windshield within the interior of the vehicle. Theimaging section 12101 provided to the front nose and the imaging section12105 provided to the upper portion of the windshield within theinterior of the vehicle obtain mainly an image of the front of thevehicle 12100. The imaging sections 12102 and 12103 provided to thesideview mirrors obtain mainly an image of the sides of the vehicle12100. The imaging section 12104 provided to the rear bumper or the backdoor obtains mainly an image of the rear of the vehicle 12100. Theimaging section 12105 provided to the upper portion of the windshieldwithin the interior of the vehicle is used mainly to detect a precedingvehicle, a pedestrian, an obstacle, a signal, a traffic sign, a lane, orthe like.

Incidentally, FIG. 9 depicts an example of photographing ranges of theimaging sections 12101 to 12104. An imaging range 12111 represents theimaging range of the imaging section 12101 provided to the front nose.Imaging ranges 12112 and 12113 respectively represent the imaging rangesof the imaging sections 12102 and 12103 provided to the sideviewmirrors. An imaging range 12114 represents the imaging range of theimaging section 12104 provided to the rear bumper or the back door. Abird’s-eye image of the vehicle 12100 as viewed from above is obtainedby superimposing image data imaged by the imaging sections 12101 to12104, for example.

At least one of the imaging sections 12101 to 12104 may have a functionof obtaining distance information. For example, at least one of theimaging sections 12101 to 12104 may be a stereo camera constituted of aplurality of imaging elements, or may be an imaging element havingpixels for phase difference detection.

For example, the microcomputer 12051 can determine a distance to eachthree-dimensional object within the imaging ranges 12111 to 12114 and atemporal change in the distance (relative speed with respect to thevehicle 12100) on the basis of the distance information obtained fromthe imaging sections 12101 to 12104, and thereby extract, as a precedingvehicle, a nearest three-dimensional object in particular that ispresent on a traveling path of the vehicle 12100 and which travels insubstantially the same direction as the vehicle 12100 at a predeterminedspeed (for example, equal to or more than 0 km/hour). Further, themicrocomputer 12051 can set a following distance to be maintained infront of a preceding vehicle in advance, and perform automatic brakecontrol (including following stop control), automatic accelerationcontrol (including following start control), or the like. It is thuspossible to perform cooperative control intended for automated drivingthat makes the vehicle travel automatedly without depending on theoperation of the driver or the like.

For example, the microcomputer 12051 can classify three-dimensionalobject data on three-dimensional objects into three-dimensional objectdata of a two-wheeled vehicle, a standard-sized vehicle, a large-sizedvehicle, a pedestrian, a utility pole, and other three-dimensionalobjects on the basis of the distance information obtained from theimaging sections 12101 to 12104, extract the classifiedthree-dimensional object data, and use the extracted three-dimensionalobject data for automatic avoidance of an obstacle. For example, themicrocomputer 12051 identifies obstacles around the vehicle 12100 asobstacles that the driver of the vehicle 12100 can recognize visuallyand obstacles that are difficult for the driver of the vehicle 12100 torecognize visually. Then, the microcomputer 12051 determines a collisionrisk indicating a risk of collision with each obstacle. In a situationin which the collision risk is equal to or higher than a set value andthere is thus a possibility of collision, the microcomputer 12051outputs a warning to the driver via the audio speaker 12061 or thedisplay section 12062, and performs forced deceleration or avoidancesteering via the driving system control unit 12010. The microcomputer12051 can thereby assist in driving to avoid collision.

At least one of the imaging sections 12101 to 12104 may be an infraredcamera that detects infrared rays. The microcomputer 12051 can, forexample, recognize a pedestrian by determining whether or not there is apedestrian in imaged images of the imaging sections 12101 to 12104. Suchrecognition of a pedestrian is, for example, performed by a procedure ofextracting characteristic points in the imaged images of the imagingsections 12101 to 12104 as infrared cameras and a procedure ofdetermining whether or not it is the pedestrian by performing patternmatching processing on a series of characteristic points representingthe contour of the object. When the microcomputer 12051 determines thatthere is a pedestrian in the imaged images of the imaging sections 12101to 12104, and thus recognizes the pedestrian, the sound/image outputsection 12052 controls the display section 12062 so that a squarecontour line for emphasis is displayed so as to be superimposed on therecognized pedestrian. The sound/image output section 12052 may alsocontrol the display section 12062 so that an icon or the likerepresenting the pedestrian is displayed at a desired position.

A description has been given above of an example of the vehicle controlsystem to which the technique according to the present disclosure isapplicable. The technique according to the present disclosure isapplicable to a ranging sensor using a millimeter wave or the likeincluded in the imaging section 12031 or the like among theabove-described configurations. Application of the technique accordingto the present disclosure to an amplification circuit or the like of theranging sensor makes it possible to decrease on-resistance. It is thuspossible to measure a distance to an object with higher sensitivity.Accordingly, the microcomputer 12051 is able to perform more appropriateautomated driving or the like.

The technique according to the present disclosure has been describedabove with reference to the first and second embodiments. However, thetechnique according to the present disclosure is not limited to theabove-described embodiments and the like and various modifications arepossible.

For example, the regrowth layer 140 including the vacancy generationregion 141 may be provided only on the source electrode 150S, may beprovided only on the drain electrode 150D, or may be provided on boththe source electrode 150S and the drain electrode 150D.

In addition, the semiconductor devices 100 and 101 may be used in awireless communication apparatus in a mobile body communication systemor the like. Specifically, they may be used in an RF switch, a poweramplifier, or the like of a wireless communication apparatus having acommunication frequency in a UHF (Ultra High Frequency) band or higher.

Furthermore, not all of the configurations and the operations describedin each of the embodiments are essential to the configurations and theoperations of the present disclosure. For example, among the componentsin each of the embodiments, components not described in the independentclaims describing the most superordinate concept of the presentdisclosure should be understood as optional components.

The terms used throughout the specification and the appended claimsshould be construed as “non-limiting” terms. For example, the terms“include” or “be included” should be construed as “not limited to theexample described with the term included”. The term “have” should beconstrued as “not limited to the example described with the term have”.

The terms used herein include some terms that are used merely forconvenience of description and are not used to limit the configurationand the operation. For example, the term such as “right,” “left,”“upper,” or “lower” merely indicates a direction on the referreddrawing. Further, the terms “inner” and “outer” merely indicate adirection toward the center of the component of interest and a directionaway from the center of the component of interest, respectively. Thissimilarly applies to terms similar to the above-described terms andterms having similar meanings.

It is to be noted that the technique according to the present disclosureis able to have the following configurations. According to the techniqueof the present disclosure having the following configurations, a vacancyserving as a doner is formed in the regrowth layer below the vacancygeneration region by the vacancy generation region provided in theregrowth layer. This improves the electrical conductivity of theregrowth layer, and therefore further decreases resistance between anelectrode and two-dimensional electron gas (i.e., a channel). Effectsexerted by the technique according to the present disclosure are notnecessarily limited to the effects described here, and may be any of theeffects described in the present disclosure.

A semiconductor device including:

-   a barrier layer including a first nitride semiconductor;-   a channel layer including a second nitride semiconductor and bonded    to the barrier layer at a first surface;-   a regrowth layer including an n-type nitride semiconductor and    provided in a region dug deeper than an interface between the    barrier layer and the channel layer from a second surface of the    barrier layer, the second surface being on opposite side to the    first surface;-   a vacancy generation region including a nitrogen-capturing element    and provided in a region of the regrowth layer shallower than the    interface between the barrier layer and the channel layer; and-   a source electrode or a drain electrode provided on the regrowth    layer.

The semiconductor device according to (1) described above, in which thenitrogen-capturing element includes Ti or Al.

The semiconductor device according to (1) or (2) described above, inwhich the source electrode or the drain electrode includes thenitrogen-capturing element.

The semiconductor device according to any one of (1) to (3) describedabove, in which the vacancy generation region further includes a nitrideof the nitrogen-capturing element.

The semiconductor device according to any one of (1) to (4) describedabove, in which the regrowth layer further includes a low defect regionin a region in contact with the interface between the barrier layer andthe channel layer, the low defect region having a crystal defect densitylower than that in other regions of the regrowth layer.

The semiconductor device according to (5) described above, in which thecrystal defect density of the low defect region is lower than or equalto 1.0 × 10¹⁰/cm².

The semiconductor device according to (5) or (6) described above, inwhich the low defect region is provided to extend from the interfacebetween the barrier layer and the channel layer toward a channel layerside.

The semiconductor device according to any one of (1) to (7) describedabove, in which a band gap of the first nitride semiconductor is greaterthan a band gap of the second nitride semiconductor.

The semiconductor device according to any one of (1) to (8) describedabove, in which the second surface of the barrier layer is furtherprovided with a gate electrode with an insulation layer interposedtherebetween.

The semiconductor device according to (9) described above, in which thegate electrode is provided between the source electrode provided on theregrowth layer and the drain electrode provided on the regrowth layer.

This application claims the priority on the basis of Japanese PatentApplication No. 2020-095054 filed on May 29, 2020 with Japan PatentOffice, the entire contents of which are incorporated in thisapplication by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A semiconductor device comprising: a barrier layer including a first nitride semiconductor; a channel layer including a second nitride semiconductor and bonded to the barrier layer at a first surface; a regrowth layer including an n-type nitride semiconductor and provided in a region dug deeper than an interface between the barrier layer and the channel layer from a second surface of the barrier layer, the second surface being on opposite side to the first surface; a vacancy generation region including a nitrogen-capturing element and provided in a region of the regrowth layer shallower than the interface between the barrier layer and the channel layer; and a source electrode or a drain electrode provided on the regrowth layer.
 2. The semiconductor device according to claim 1, wherein the nitrogen-capturing element includes Ti or Al.
 3. The semiconductor device according to claim 1, wherein the source electrode or the drain electrode includes the nitrogen-capturing element.
 4. The semiconductor device according to claim 1, wherein the vacancy generation region further includes a nitride of the nitrogen-capturing element.
 5. The semiconductor device according to claim 1, wherein the regrowth layer further includes a low defect region in a region in contact with the interface between the barrier layer and the channel layer, the low defect region having a crystal defect density lower than that in other regions of the regrowth layer.
 6. The semiconductor device according to claim 5, wherein the crystal defect density of the low defect region is lower than or equal to 1.0 × 10¹⁰/cm².
 7. The semiconductor device according to claim 5, wherein the low defect region is provided to extend from the interface between the barrier layer and the channel layer toward a channel layer side.
 8. The semiconductor device according to claim 1, wherein a band gap of the first nitride semiconductor is greater than a band gap of the second nitride semiconductor.
 9. The semiconductor device according to claim 1, wherein the second surface of the barrier layer is further provided with a gate electrode with an insulation layer interposed therebetween.
 10. The semiconductor device according to claim 9, wherein the gate electrode is provided between the source electrode provided on the regrowth layer and the drain electrode provided on the regrowth layer. 